Part A | 5.2
52 Part A Marine Flora and Fauna
5.2 Marine Microalgae
Algae are a very diverse group of photosynthetic organisms other than land plants, which have been classified
into many classes, such as Cyanophyceae, Chlorophyceae, Rhodophyceae, Cryptophyceae, Dinophyceae,
Bacillariophyceae, Haptophyceae, Euglenophyceae or
Prasinophyceae. For convenience, they are referred to
as blue-green algae, green algae, brown algae, or red
algae due to the difference in composition of photosynthetic pigments. However, it is difficult to make
a clear definition of algae because even multicellular
eukaryotic microalgae (what is called seaweed) are also
included. In this section, some representative marine
microalgae are summarized to introduce their biotechnological applications.
Cyanophyceae (cyanobacteria, blue-green algae)
are oxygenic photosynthetic prokaryotes that comprise a single taxonomic and phylogenetic group.
Chloroplasts in eukaryotes evolved from endosymbiotic cyanobacteria. They show a large diversity in
their morphology, physiology, ecology, biochemistry,
and other characteristics. Typically, cyanobacteria contain chlorophyll a and phycocyanin. Three genera, i. e.,
Prochlorococcus, Prochloron, and Prochlorothrix, lack
phycocyanin and possess chlorophyll a and b [5.1].
A unicellular cyanobacterium that synthesizes chlorophyll d has also been discovered [5.2]. Marine Synechococcus and Prochlorococcus contribute largely to
global oxygen production. Cyanobacteria have gained
attention as a source of bioactive compounds and
biopolymers (polyhydroxyalkanoates (PHA)s) [5.3].
Bioactive compounds isolated from marine cyanobacteria were summarized by Burja et al. [5.4] and Takeyama
and Matsunaga [5.5]. Several strains of cyanobacteria (Synechococcus elongates and Anabaena variabilis)
have been reported to produce long-chain alkanes
and alkenes [5.6]. These findings make cyanobacterial
alkane and alkenes a promising source of biofuels [5.7].
Two enzyme families that are responsible for straightchain hydrocarbon production in cyanobacteria have
recently been identified as an acyl–acyl carrier protein reductase (AAR) and an aldehyde-deformylating
oxygenase (ADO). These enzymes convert fatty acid
intermediates to alkanes and alkenes. This discovery of the cyanobacterial alkane biosynthesis indicates possibilities for optimizing the biodiesel production in cyanobacterial strains with modest gains in
alkanes [5.8].
Chlorophyceae, which are one of the classes of
green algae, possess chlorophyll a and b, the same
predominant photosynthetic pigments as those of land
plants. Chlorophyceae form starch in the chloroplast
as a storage product of photosynthesis. Especially,
Chlamydomonas reinhardtii has been used as a representative eukaryotic microalgae for biology and molecular biology studies. Chloroplast transformation was
firstly achieved in C. reinhardtii [5.9]. Some species
of Chlorophyceae are found in the marine environment. A marine species of Chlorophyceae, Dunaliella
has been cultivated commercially for food supplements
and ˇ-carotene production [5.10]. Chlorella, which is
a genus of single-cell and chlorophyll a/b-containing
algae, belongs to the phylum Chlorophyta. It has been
known as a potential food resource because of its high
content of protein and other nutrients. Miura and others [5.11] reported that Chlorella sp. NKG 042 401
contains 10% -linolenic acid (C18:3), which is present
in the cells mainly in the form of galactolipids. In Euglenophyceae, the genus Euglena is well known. The
chloroplast of Euglena originated from the eukaryotic
green algae and contains chlorophyll a and b. Although
most species are found in freshwater environments,
some species also occur in marine environments.
Bacillariophyceae (diatoms) possess chlorophyll
a and c, and fucoxanthin as the major carotenoid.
Diatoms are widely used as feed in mariculture/aquaculture [5.12, 13]. Chaetoceros calcitrans,
Chaetoceros gracilis, Chaetoceros muelleri, Skeletonema costatum, and Thalassiosira pseudonana are
commonly used as live feed for all growth stages of
bivalve molluscs (e.g., oysters, scallops, clams, and
mussels), for crustacean larvae, and for zooplankton
used as feed for larvae. The genera Navicula, Nitzschia,
Cocconeis, and Amphora also are used to feed juvenile abalone. They store energy either as lipids or as
chrysolaminarin. Most diatoms have a high content
of eicosapentaenoic acid (EPA) 20 W 5 (n-3). Phaeodactylum tricornutum and Nitzschia laevis have been
especially investigated for EPA production. In addition,
EPA production by diatoms was reviewed recently by
Lebeau and Robert [5.14, 15]. Recent advances in heterotrophic production of EPA by microalgae were also
reviewed by Wen and Chen [5.16].
The cells of Haptophyceae are brownish or
yellowish-green and contain chlorophylls a/c and
carotenoids such as ˇ-carotene, fucoxanthin, diadinoxanthin, and diatoxanthin. The cells are commonly
covered with scales made mainly by carbohydrates or
calcium bicarbonate. Many species known as coccol-
52 Part A Marine Flora and Fauna
5.2 Marine Microalgae
Algae are a very diverse group of photosynthetic organisms other than land plants, which have been classified
into many classes, such as Cyanophyceae, Chlorophyceae, Rhodophyceae, Cryptophyceae, Dinophyceae,
Bacillariophyceae, Haptophyceae, Euglenophyceae or
Prasinophyceae. For convenience, they are referred to
as blue-green algae, green algae, brown algae, or red
algae due to the difference in composition of photosynthetic pigments. However, it is difficult to make
a clear definition of algae because even multicellular
eukaryotic microalgae (what is called seaweed) are also
included. In this section, some representative marine
microalgae are summarized to introduce their biotechnological applications.
Cyanophyceae (cyanobacteria, blue-green algae)
are oxygenic photosynthetic prokaryotes that comprise a single taxonomic and phylogenetic group.
Chloroplasts in eukaryotes evolved from endosymbiotic cyanobacteria. They show a large diversity in
their morphology, physiology, ecology, biochemistry,
and other characteristics. Typically, cyanobacteria contain chlorophyll a and phycocyanin. Three genera, i. e.,
Prochlorococcus, Prochloron, and Prochlorothrix, lack
phycocyanin and possess chlorophyll a and b [5.1].
A unicellular cyanobacterium that synthesizes chlorophyll d has also been discovered [5.2]. Marine Synechococcus and Prochlorococcus contribute largely to
global oxygen production. Cyanobacteria have gained
attention as a source of bioactive compounds and
biopolymers (polyhydroxyalkanoates (PHA)s) [5.3].
Bioactive compounds isolated from marine cyanobacteria were summarized by Burja et al. [5.4] and Takeyama
and Matsunaga [5.5]. Several strains of cyanobacteria (Synechococcus elongates and Anabaena variabilis)
have been reported to produce long-chain alkanes
and alkenes [5.6]. These findings make cyanobacterial
alkane and alkenes a promising source of biofuels [5.7].
Two enzyme families that are responsible for straightchain hydrocarbon production in cyanobacteria have
recently been identified as an acyl–acyl carrier protein reductase (AAR) and an aldehyde-deformylating
oxygenase (ADO). These enzymes convert fatty acid
intermediates to alkanes and alkenes. This discovery of the cyanobacterial alkane biosynthesis indicates possibilities for optimizing the biodiesel production in cyanobacterial strains with modest gains in
alkanes [5.8].
Chlorophyceae, which are one of the classes of
green algae, possess chlorophyll a and b, the same
predominant photosynthetic pigments as those of land
plants. Chlorophyceae form starch in the chloroplast
as a storage product of photosynthesis. Especially,
Chlamydomonas reinhardtii has been used as a representative eukaryotic microalgae for biology and molecular biology studies. Chloroplast transformation was
firstly achieved in C. reinhardtii [5.9]. Some species
of Chlorophyceae are found in the marine environment. A marine species of Chlorophyceae, Dunaliella
has been cultivated commercially for food supplements
and ˇ-carotene production [5.10]. Chlorella, which is
a genus of single-cell and chlorophyll a/b-containing
algae, belongs to the phylum Chlorophyta. It has been
known as a potential food resource because of its high
content of protein and other nutrients. Miura and others [5.11] reported that Chlorella sp. NKG 042 401
contains 10% -linolenic acid (C18:3), which is present
in the cells mainly in the form of galactolipids. In Euglenophyceae, the genus Euglena is well known. The
chloroplast of Euglena originated from the eukaryotic
green algae and contains chlorophyll a and b. Although
most species are found in freshwater environments,
some species also occur in marine environments.
Bacillariophyceae (diatoms) possess chlorophyll
a and c, and fucoxanthin as the major carotenoid.
Diatoms are widely used as feed in mariculture/aquaculture [5.12, 13]. Chaetoceros calcitrans,
Chaetoceros gracilis, Chaetoceros muelleri, Skeletonema costatum, and Thalassiosira pseudonana are
commonly used as live feed for all growth stages of
bivalve molluscs (e.g., oysters, scallops, clams, and
mussels), for crustacean larvae, and for zooplankton
used as feed for larvae. The genera Navicula, Nitzschia,
Cocconeis, and Amphora also are used to feed juvenile abalone. They store energy either as lipids or as
chrysolaminarin. Most diatoms have a high content
of eicosapentaenoic acid (EPA) 20 W 5 (n-3). Phaeodactylum tricornutum and Nitzschia laevis have been
especially investigated for EPA production. In addition,
EPA production by diatoms was reviewed recently by
Lebeau and Robert [5.14, 15]. Recent advances in heterotrophic production of EPA by microalgae were also
reviewed by Wen and Chen [5.16].
The cells of Haptophyceae are brownish or
yellowish-green and contain chlorophylls a/c and
carotenoids such as ˇ-carotene, fucoxanthin, diadinoxanthin, and diatoxanthin. The cells are commonly
covered with scales made mainly by carbohydrates or
calcium bicarbonate. Many species known as coccol-